This invention relates to railroad cars, and more particularly to protecting covered hopper cars from vacuum failure during unloading.
A covered hopper cars typically has partitions dividing the car into separate compartments, with each compartment having one or more openings for loading the car. The openings are typically defined by a coaming which extends upward on the top wall of the car, and may comprise, e.g., elongated rectangular openings or circular hatches. Where vacuum discharge gates are employed, materials are typically unloaded by applying a vacuum conveying line to a nozzle at the bottom of each compartment. The primary air flow for the vacuum line comes from outside the car, but the displacement of the lading creates a vacuum within the car, requiring venting of the car. If the partial vacuum is not relieved, it can reach a point where the car""s body is damaged. Failure to vent the vacuum also reduces the efficiency of the unloading process. Where gravity or gravity-pneumatic gates are employed, similar problems exist.
In the past, venting during unloading to prevent vacuum failure has commonly been achieved by opening at least one hatch cover on each compartment. However, this is somewhat inefficient in that it requires workers to climb to the top of the car to manually open each hatch. Venting may also be required after cleaning. If a compartment is cleaned with hot water or steam and the hatch is closed and sealed before the car interior has cooled to ambient temperature, subsequent cooling may result in a temperature differential sufficient to cause inward buckling of the walls of the car.
In recent years, two alternatives have been explored for venting of covered hopper cars: vents on the end walls of the cars and vented hatch covers. Each approach has problems.
Among the problems that must be addressed in providing a commercially viable vent in a hatch cover or end wall are removal of contaminants from the airflow during unloading, and physical access for maintenance. If filters or screens are used over the vents, sufficient physical access must be provided to enable railroad personnel to change or maintain them without undue difficulty. Consideration must also be given to the railcar""s exposure to high winds, and high rates of airflow relative to the hatch covers during travel. Precipitation, dust, and other particles may be driven into the cars, contaminating the cargo, absent adequate filtration, particularly during conditions of high winds, rain, snow or other inclement weather.
Another problem that must be addressed by any venting solution for cars where high standards of purity apply, such as cars carrying plastic pellets, is preventing retention of any lading material. Retention of even a small quantity of a load in a vent, hatch cover or other component of a railcar may result in contamination of a subsequent load of a different material.
Vented hatch covers have not generally included filters capable of preventing fine particulates from contaminating the cargo. Accordingly, separate filters have generally been used to cover the openings underneath the vented hatch covers. These filters are similar in configuration to shower caps, with elastic being provided to hold them in place to cover the hatches after the covers have been raised. A significant disadvantage of these filters is that they must be removed when loading material into the car interior, and may have to be replaced with each load. It has been difficult to provide a commercially viable alternative due at least in part to the difficulties in providing a filter arrangement which can provide required volume flow rate during unloading without violating overhead clearance requirements, and which can be easily changed or serviced. Limited space is available adjacent the hatches, so bulky filter arrangements cannot be used. However, if the cross-section of the airflow path through a filter element is not large enough, the pressure drop across the filter element may be unacceptably high and cause inward buckling of the railcar sidewalls in response to vacuum build-up in the railcar interior.
Additional problems with vents in the end walls of covered hopper cars are that they provide airflow only to the end compartments, and due to difficult access, are very likely not to be maintained, thereby endangering the car body when the filter becomes clogged. Some structure may be required to support workers conducting maintenance. In the past, small breather holes of about 1 in. diameter have been provided on the ends of covered hopper cars carrying cement. These cars do not have seals between their interior compartments. A piece of angle or other protective structure is welded to the wall adjacent the hole to shield it from rainwater. Small breather holes have also been provided in hatch coamings, in conjunction with wire mesh to exclude insects. The breather holes permit sufficient airflow to compensate for changes in ambient temperature, but do not permit sufficient airflow to replace displaced cargo volume. Also, many cars have sealed interior compartments which cannot be vented by end wall vents.
There is a need in the industry for an improved commercially viable means to enable unloading of covered hopper cars which avoids the need to open the hatches during unloading, and which avoids contamination of the cargo both during vacuum discharge and at other times.
The invention provides a new approach to venting of covered hopper cars in which sufficient airflow is provided through an opening in the side of the coaming to prevent vacuum failure during unloading, without the need to open or vent any of the hatch covers. A housing or shield may extend outward from the side of the coaming and may contain one or more filter elements.
In a preferred embodiment, air intakes are provided in a sheltered location to reduce or eliminate intake of debris or precipitation. To this end, in the preferred embodiment, one or more openings or slots between the housing and the coaming may provide for the intake of air. Air flows through the slots into the housing, then through a filter element, then through the opening in the coaming and into the hopper car interior.
The filter elements preferably are removable so as to be replaceable. The housing is preferably attached to the outside of the coaming in a manner that facilitates removal and replacement of the filter element.
For cars intended to be used for transportation of loads in which control of contaminants does not require filtration, e.g., cement, the filter may be eliminated.
The opening in the coaming is sized to permit sufficient air flow into the car interior to replace the lading during unloading of the compartment, without an unduly high pressure drop under typical commercial unloading conditions. If greater air flow is required, one or more additional openings and housings may be provided in the coaming. The opening and housing are preferably located below the top edge of the coaming so as not to interfere with opening and closing of the cover. The cover need not be opened during unloading. Indeed, after loading, the cover can be sealed shut, only to be opened when the car is to be loaded with another cargo or cleaned. The vented coaming of the invention does not encroach into required overhead railroad clearances and is compact in size so as not to interfere with walking clearances for railroad workers on the covered hopper car.
Preferably, the vented coaming includes a throat element adapted to contact and seal against the opening in the coaming. The interior of the throat preferably defines an air passage through which air travels to the car interior. A screen may be positioned in the throat to provide protection against inflow of contaminants where a filter is not employed, and/or to prevent plastic pellets or other particulates from exiting the hatch. In cases where a lading such as plastic pellets having stringent requirements of purity is involved, the screen may prevent pellets from entering the throat or housing, which could result in contamination of future ladings by later displacement of such particulates.
Vented coamings in accordance with the invention may be installed as original equipment or, if desired, existing coamings may be modified to provide venting in accordance with the invention.
While the embodiments shown in the accompanying drawings include circular hatch rings, in other embodiments the invention may be employed with straight-sided rectangular trough hatches, or hatches of other shapes.